1. Field of the Invention
This invention relates to new and useful improvements in earth drilling apparatus and more particularly to an improved system of control for earth drilling apparatus by controlling the application of braking force to the drum which feeds out the drill line and controls the lowering of the drill pipe during the drilling operation.
2. Brief Description of the Prior Art
In earth drilling, particularly the drilling of oil and gas well, the control of the drilling operation has usually been accomplished manually. In a conventional drilling rig, there is a draw works which is powered by an engine and operates most of the motor driven portions of the rig. The draw works has a drum with a drill line wound on it which is fed off to lower drill pipe as the drilling is accomplished. The drill line is looped through a crown block and a traveling block in a double pulley relationship and the end of the line is connected to a fixed point and called the deadline.
As the pipe is lowered into the well during drilling, the weight of the pipe string on the drill bit is measured by the tension in the drill line. The tension in the drill line is commonly measured by a pressure sensor which converts tension to weight indication through a hydraulic line extending to a bit weight gage on the drilling console. The rate of feed out of the drill line from the drum controls the bit weight and to a large extent the rate of drilling. The rate of feed out of drill line from the drum is controlled by a hand brake operated by a conventional brake lever. In manually-operated drilling rigs the driller has to monitor the operation of the equipment and operate the brake from time to time in response to the indications of the bit weight gage to control the rate of feed out of the drill line and thus attempt to keep a fairly constant bit weight.
In recent years there have been developed a number of automatic drilling machines. These machines are automatic in the sense that they provide some form of automatic control over the equipment. The commercially available automatic drillers have been marketed under the names BEAR, NATIONAL, STEWART AND STEVENSON, and SATELLITE. These automatic drillers operate from the air supply of the drilling rig enroute to the drillers control station. The components involved are mainly air clutches with various types of air dump valves to exhaust used air. These devices which use up and exhaust compressed air that is needed in the operation of the drilling rig are considered wasteful of the compressed air which often has to be reused in order to keep the drilling rig going.
More recently, some automatic drillers have been introduced which operate from special weight or tension sensors which are connected into the dead line and which control the application of compressed air to various control valves or clutches. Again, these devices have been objected to by many drillers as being wasteful of compressed air and being mechanically inefficient. There have also been a rather large number of instances of mechanical failure which have led to the disconnection of many of the automatic drillers from rigs where they have been installed.
Several patents have been noted which do not disclose any of the aforementioned automatic drillers but which are somewhat relevant in that they disclose some form of control for a drilling operation.
Klima U.S. Pat. No. 3,593,807 discloses a mining blast hole drilling apparatus having a hydraulic mechanism for forcing the drill bit into the ground and a controlled system for adjusting the drilling operation the controlling hydraulic pressure applied to the drill string.
Bromell U.S. Pat. No. 3,609,919 discloses a system for controlling a mining or blast hole drill bit by sensing dead weight and controlling the application of pressure to the drill bit.
Dower U.S. Pat. No. 3,893,525 discloses a system for controlling a drilling operation having manual control at the rig and a remote controller for controlling the operation away from the rig.
Barron U.S. Pat. No. 3,917,230 discloses a well drilling control system using various load sensing and movement sensing transmitters to adjust the weight on the drill bit to compensate for movement of a barge or platform in an offshore drilling operation.
The aforementioned patents, and the commercially available automatic drillers described above, do not suggest a drilling control system which gives a substantially instantaneous and positive control of the bit weight by a positive control of the brake controlling the feed out of drill line from the drum on the draw warks.